The present application relates to an ignition plug for an internal combustion engine, more particularly to a ground electrode which is a part of such an ignition plug.
Generally, the ground electrode is in the form of a metallic bar extending from one side of the annular component forming the threaded shell of the plug, the bar being bent such to be L-shaped towards the axis of the plug and located within an appropriate distance above the central electrode which is generally concentric with the said axis. This bar is of rectangular cross section. The electrode is connected to the ground through the threaded shell which, in use, is in contact with the engine.
It is known that one can vary the form and configuration of the ground electrode in order to obtain an effect on the electrical spark and/or the ignition and/or the movement and turbulence of gases in the cylinder of an engine.
Ground electrodes of complicated forms and configurations, e.g. annular around the central electrode, or with openings, grooves, slots or in the form of a fork, have been disclosed in U.S. Pat. No. 4,401,915 and French patent application No 2,440,100. In PCT patent application WO81/01918 there is disclosed a spark plug with several L-shaped electrodes which have been twisted so to give them the form of blades of a propellor. This configuration would afford favorable swirling movements of the flame front.
U.S. Pat. No. 2,845,566 discloses a spark plug with a flat, ribbon-shaped electrode downwardly and inwardly twisted at an angle of slightly less than ninety degrees. The ribbon edge terminates in a sharp nose and lies within the axial projection of the central electrode. A minimum baffle or obstruction of the flow of the gases in both direction is claimed. The spark plug is claimed to be more erosion-resistant than classical spark plugs.
It is also known to improve the resistance to erosion of the ground electrode by giving a different configuration to the cross section of the ground electrode. U.S. Pat. No. 4,970,426 (Bronchart) discloses a ground electrode which has a cross section such that the surface of the ground electrode which is located nearest to the bottom of the central electrode is larger than the surface of the ground electrode which is located farthest away from said bottom end of the central electrode, the spark being viewed with the electrodes pointing downward. In one embodiment the smaller surface is reduced to a line, the cross section being then triangular. It is also disclosed that the lateral sides of the triangular cross section may be curved.